Synthetic diester lubricating oils



SYNTHETIC DIESTER LUBRICATING OILS Application October 12, 1953 Serial No. 385,678

Claims priority, application Great Britain November 19, 1952 15 Claims. (Cl. 25242.7)

No Drawing.

This invention relates to novel synthetic lubricating oils capable of functioning over a wide temperature range, and their preparation. More particularly, it relates to novel synthetic lubricating oils of the ester type and their preparation.

Lubricants for use in aircraft and in gas turbines require special properties which are not possessed by conventional lubricants. Thus, they must possess a very high viscosity index in order to provide adequate lubrication over a wide range of temperatures. They must have a low poor point in order that they may function at low temperatures and high flash points to avoid risk of fire at high temperature operation and loss of lubricant by evaporation.

It has already been proposed to use certain types of synthetic esters as lubricating oils and as bases for lubricating compositions intended for use in aircraft instruments and other fine instruments, such as galvanometers, gun directing equipment, clock and gyro compasses. These esters vary from simple esters of dior polycarboxylic acids to complex esters such as those derived from half esters or others of glycols and dior polycarboxylic acids. However, many of these esters suffer from the defect that they tend to supercool below their true melting point and are thus unreliable for low temperature lubrication since a supercooled liquid is unstable and may solidify. Attempts have been made to avoid this undesirable phenomenon by the use of a mixture of the esters but in general such mixtures still exhibit supercooling properties.

It has now been found that if a mixture of at least two of certain of these esters is subjected to heat treatment with an alkali metal, a product can be obained which exhibits no supercooling properties and is, therefore, highly suitable for low temperature lubrication. Moreover, the products of the present invention have a higher viscosity and a lower true melting point than the mixture of esters used as starting material. Further, the products of this invention have a higher loadcarrying capacity than the ester mixture from which they are obtained, and they have a load-carrying capacity considerably higher than that of equiviscous mineral lubricating oils. The products of the present invention also have high flash points and low volatility.

Described more specifically, there are provided by the present invention, synthetic lubricating oils prepared by subjecting a mixture of at least two normally liquid diesters of dicarboxylic acids in which the carboxyl radicals are separated from each other by at least 1 carbon atom and of alcohols containing at least 3 carbon atoms, preferably from about 4 to about 20 carbon atoms, to an elevated temperature in the presence of an alkali metal.

According to a specific embodiment of the invention, there are provided synthetic lubricating oils prepared by subjecting a mixture of at least two normally liquid diesters of dicarboxylic acids in which the carboxyl radi nited States Patent cals are separated from each other by at least 1 carbon atom and of alcohols containing at least 3 carbon atoms, preferably from about 4 to about 20 carbon atoms, to an elevated temperature in the presence of an alkali metal, acidifying the reaction mixture to liberate organic acids from alkali metal salts thereof formed as by-products of the reaction, and esterifying the liberated organic acids with a polyhydric alcohol.

The exact mechanism of the reaction which occurs during the above-described process is not fully understood. Something more than simple ester interchange occurs because the mixtures of esters which would result from such simple ester interchange still exhibit supercooling. Furthermore, the use of other ester interchange catalysts, such as litharge or alkali metal alcoholates, in place of the alkali metal does not give products free from the supercooling phenomenon. It also appears that something more than the Claisen condensation occurs because if a single ester of the type described above is subjected to heating in the presence of an alkali metal, again the product exhibits supercooling properties.

The esters which constitute the starting materials in the above-described process are those which satisfy the following general structural formula:

wherein R is a hydrocarbon radical of at least 1 carbon atom, preferably from about 4 to about 12 carbon atoms, R and R are hydrocarbon radicals of at least 3 carbon atoms, preferably from about 4 to about 20 carbon atoms, and preferably R is the same as R and R and R are hydrogen atoms or hydrocarbon substituents.

The acids from which the above-described esters are derived can be either saturated dicarboxylic acids or unsaturated dicarboxylic acids. Suitable acids include: malonic acid; ethylmalonic acid; succinic acid; methylsuccinic acid; 1,1-diethylsuccinic acid; 1,2-diethylsuccinic acid; glutaric acid; methylglutaric acid; ethylglutaric acid; propylglutaric acid; isopropylglutaric acid; butylglutaric acid and its isomers; amylglutaric acid and its isomers; dimethylglutaric acid; methylethylglutaric acid; methylpropylglutaric acid; methylbutylglutaric acid and its isomers; diethylglutaric acid; ethylpropylglutaric acid; adipic acid; Z-methyladipic acid; 2-ethyladipic acids; 2-butyladipic acids; 2,2-dimethyladipic acid; 2,3-dimethyladipic acid; 2-methyl-2-ethyladipic acid; 2-methyl-3-ethyladipic acid; Z-methyl-2-isopropyladipic acid- 2,2,4- and 2,4,4- trimethyladipic acids; pimelic acid; Z-methylpimelic acid; B-methylpimelic acid; 2-ethylpimelic acid-3-ethylpimelic acid; 2- and 3-propylpimelic acids; 2- and 3-isopropylpimelic acids; 2,2- and 2,3-dimethylpirnelic acids; 2- methyl-Z-ethylpimelic acid; 2-methyl-3-ethylpimelic acid; 3-methyl-3 -ethylpimelic acid; 2-ethyl3-methylpimelic acid; 2,2,3-trimethylpimelic acid; 2,3,4-trimethylpimelic acid; 1,2,5-trimethylpimelic acid; .suberic acid; methyland ethyl-suberic acids in which the methyl or ethyl groups may be in positions 2, 3, 4 or 5; and methylethylsu'beric acids, wherein the methyl and ethyl groups are in positions 2, 3, 4 or 5; azelaic acid; methylazelaic acids; ethylazelaic acids; sebacic acids; methylsebacic acids; ethylsebacic acids; undecanedioic acids; dodecanedioic acids; and the like. Aromatic dicarboxylic acids, such as phthalic acid, are also suitable.

The alcohols from which the above esters are derived can be either aliphatic, araliphatic or cycloaliphatic alcohols of at least 3 carbonatoms, and preferably from about 4 to about 20 carbon atoms. The saturated aliphatic alcohols are preferred. Both straight-chain and branched-chain saturated aliphatic alcohols are suitable,

,3 a but the branched-chain alcohols are preferred. Suitable alcohols include the alkanols, such as butanol, isobutanol;

tert-butanol; l-methylpropanol; pentanol; Z-methylbutanol; 3-methylbutanol; 1- and 2-ethylpropanols; 2,2- and 1,2-dirnethylpropanols; hexanol; 2-, 3- and" 4=methylpentanols; 2,2-dimethylbutanol; 2,3-dimethylbutanol; 2- ethylbutanol; B-ethylbutanol; 2-meth'yl-2-ethylpr'opanol; heptanol; 2-, 3-, 4- and 5-methylhexanols;-2-, 3- and 4-ethylpentanols; 1-methyl-2-ethylbutanol; 2-methyl-3- ethylbutanol; octanol; 2-,"3- and 4-ethylhexanols; 2-, 3-, 4-, and S-methylheptanols; 2,2-dimethylhexanol; 3,3-dimethylhexanol; 2,4 dimethylhexanol; 1 isopropyl-3- methylbutanol; nonanol; 3,3-diethylpentanol; 2-ethyl-3- methylhexanol; 3,5,5 -trimethylhexanol; 2-isopropyl-4- butyloctanol; 3-butyldecanol; 2-butyl-5-propyl-7-ethylundecanol, and the like; aralkanols, such as benzyl alcohol and phenylethyl alcohol; and cycloalkanols, such as oyclopentanol, cyclohexanol and methylcyclohexanol; and the like.

The most suitable esters for use in the present invention are the esters of saturated aliphatic dicarboxylic acids in which the carboxyl radicals are separated by a chain of from about 4 to about 12 carbon atoms, and preferably from about 4 to about 8 carbon atoms, and alkyl alcohols, preferably branched-chain alcohols, having from about 4 to about 20 carbon atoms, specifically from about 7 to about 9 carbon atoms. Commercial mixtures of alcohols containingsubstantial proportions of branched-chain I According to a preferred embodiment of the invention, the reaction mixture, upon completion of the treatment with the alkali metal, is acidified to liberate organic acids from their alkali metal salts. The liberated organic acids are then esterified in situ with a polyhydric alcohol, preferably a dihydric alcohol. In this case, acidification of the reaction mixture can be effected by means of a concentrated mineral acid, such as concentrated sulfuric acid or hydrogen chloride gas, any excess of which will function as the esterification catalyst in the subsequent esteriiication step. However, it is preferred to employ dilute acids for the acidification step and to separate the resulting aqueous or dilute acid layer before the esterification step. Alcohol by-products can be removed from the mixture before the esterification step, but it is generally preferred to leave them in the mixture during the esterification.

The polyhydric alcohol used to esterify the liberated organic acids in the reaction mixture is preferably a saturated aliphatic dihydric primary alcohol of from about 2 to about carbon atoms. Typical examples of suitable alcohols are the alkane diols such as ethylene glycol;

1,2-dihydroxyprop ane; 1,3-dihydroxyprop ane; 1,2-dihydroxybutane; 1,4-dihydroxybutane; 1,2-dihydroxypentane; 1,4-dihydroxypentane; 1,5-dihydroxypentane; 2,3-dihydroxypentane; 1,2 dihydroxyhexane; 1,4 dihydroxyhexane; 1,5-dihydroxyhexane; 1,6-dihydroxyhexane; 2,3-

dihydroxyhexane; 2,4-dihydroxyhexane; 2-methyl-2,4-dialcohols, such as alcohols obtained by the 0x0 process,

are also suitable.

Typical specific liquid esters which can be employed are: di(2-methylheptyl) adipate; di(3,5,5-trimethylhexyl) adipate and amount of alkali metal employed depends on the duration and temperature of heating of the esters. an amount between about 0.5% and about 2.5,% based on the'weightof the ester mixture, is satisfactory.

In general,

The temperature to which the reaction mixture is heated is preferably above the melting point of the alkali metal used and below the distillation or decomposition temperature of the diesters being treated. Generally, using sodium, a temperature between about 100 and 200 C. is satisfactory. The duration of heating is dependent on the other conditions employed. The heating should be continued until the product, stripped of metal compounds and any free alcohol formed, no longer exhibits supercooling. In general, a period of 1 to 10 hours sufiices.

Preferably the diester mixture is subjected to heating with the alkali metal in an oxygen-free atmosphere, e. g., in a nitrogen atmosphere, and to obtain best results, the reaction mixture should be agitated during the heat treatment.

On completion of the heat treatment with'the alkali metal, the reaction mixture is acidified to liberate organic acids from their alkali metal salts which are formed as by-products of the reaction. This may be carried out by treatment with a mineral acid, such as dilutesulfuric acid or hydrochloric acid. The resulting aqueous acid layer is then separated from the diester-mixture. The liberated organic acids can be removed from the product by water washing. Any alcohols formed as by-products of 'the reaction can be stripped from the product by distillation. For some uses, the presence of small quantities of alcohols in the product may not be harmful, in which case the stripping is unnecessary.

' action mixture.

' moved by distillation.

hydroxypentane; 1,2-dihydroxyoctane; 2,7-dihydroxyoc tane; 4,5-dihydroxyoctane; 1,2-dihydroxyhexadecane; 1,2-dihydroxyeicosane and the like; the alkane triols such as glycerol; l-methylglycerol; 1,2,4-trihydroxybutane; 1,3,3-trihydroxybutane; l-ethylglycerol; 1,2,4-trihydroxypentane; 1,2,5-trihydroxypentane; 1,3 ,S-trihydroxypentane; 2,3,4-trihydroxypentane, and the like;

polyhydric alcohols such as erythritol, pentaerythritol, sorbitol and mannitol; and the polyalkylene glycols such as diethylene glycol, triethylene glycol, dipropylene 4O glycol and dibutylene glycol, and the like.

The amount of polyhydric alcohol employed in the esterification step is generally in excess of that equivalent to the amount of free organic acids present in the re- However, an equivalent amount or less of the alcohol can be used if desired. The esterification is effected in the presence of one of the usual esterification catalysts, such as concentrated sulfuric acid, hydrogen chloride or p-toluenesulfonic acid. Preferably a volatile organic diluent, such as a petroleum spirit, benzene, toluene or xylene, is employed so that the water formed in the esterification can be removed by azeotropic distillation.

After the esterification is complete, the esterification catalyst and any remaining free organic acids are Washed from the product. Any alcohol present can be re- For some uses the presence of small quantities of alcohols in the product may not be harmful, in which case alcohol removal is unnecessary.

For any given mixture of diesters used as starting material, heating of the diester mixture in the presence of an alkali metal followed by esterification of free organic acids with a polyhydric alcohol yields a product which has a higher viscosity than the product obtained by the heat-treatment alone.

The mixture of diesters subjected to the process of the present invention can be chosen to give a synthetic lubrieating oil having properties suitable for the particular purposes for which it is to be used. Thus, for preparing a base for an aircraft gas turbine lubricating composition, a mixture of di(3,5,5-trimethylhexyl) sebacate and di(2-ethylhexyl) sebacate, particularly in a weight ratio of from about :20 to about :5, a particularly suitable starting mixture.

The following examples are illustrative of the present invention. The parts referred to in the examples are partsby weight except where otherwise stated, the relation of parts by weight to parts by volume being that of the kilogram to the liter. It is to be understood that the following examples are not to be considered as limiting the specification and claims in any manner.

6 trimethylhexyl) pimelate and 25 parts of di(3-ethylhexyl) adipate was subjected to the process of Example I. The product was an excellent synthetic lubricating oil.

EXAMPLE I 5 EXAMPLE VII One part of sodium was added to a mixture of 85 parts A mixture of diesters comprising 80 parts of di(3,3 of di(3,5,5-trimethylhexyl) sebacate and 15 parts of didllsopropylhexyl) plmelate and 20 parts of dl(3,3-d1- (2-ethylhexyl) sebacate at room temperature. The remethylhexyl) azelate was sub ected to the process of Exaction vessel flushed out with nitrogen and the mixture 10 ample I. The product was an excellent synthetic lubriwas heated with stirring to 150 C., at which temper- 051mg oil. ature it was maintained for 1 /2 hours. The mixture was The pr pettles of the products of Examples I through then allowed to cool to 80-85 0., and hydrochloric V r elven m Table I- T pr p r s of h prod c acid (10 parts by volume of concentrated acid in 90 0f the present invention are compared w1th those of the parts by volume of water) was added with stirring. folloW ng products: When cold, the mixture was diluted with 100 parts by n untreated mixture of 85 parts of d1(3,5,5-tnvolume of a gasoline fraction boiling between 70 C. and y y sebacate and 15 Parts Of Y Y 95 C. The resulting organic layer was separated, washed sebacate with 100 parts by volume of 2 N hydrochloric acid and mlifed ester P 'FR y esterlflflng then with 10 parts by volume of water and dried over an- Sebaclc l Wllh a IIllXtufe comalnmg y Welght hydrous magnesium sulfate. The gasoline was removed of 3,5,5-trlmthylhexallol and 15% y Welght 0f y by distillation under reduced pressure and the residue was hexanolstripped at 230 C. at a pressure of 1 mm. Hg in an at- A prQduct PYFPaTed as ExamP1e I f employmg mosphere of carbon dioxide. The residue was cooled 5 1 g x piggf i gi gzig i g g i n usmg 1 23 filtered to yleld an excellent Synthetic lubncatmg stead of the mixture of diesters specified, 100 parts of di- (3,5,5-trimethylhexyl) sebacate.

EXAMPLE H E. A product prepared as in Example I using instead The process of Example I was repeated, using a mixof 1 part of sodium the equivalent weight of sodium ture of 95 parts of di(3,5,5-trimethylhexyl) sebacate and nonylate.

Table I Viscosity in Centistokes Flash Melting Product KVI Point F.) Point, Cooling Curve (open cup 0. At At 210 F. 100 F.

Example I 5. 56 25. 57 Satisfactory. Example 11..... 5. 83 27. 81 Do. Example III 5. 21 23. 82 Do. Example IV 6.21 22. 97 Do. Example V 3. 54 14.06 Do. A 4.3 17.62 Showssupercooling. B 4.21 17.05 D0. 0 4. 32 17.79 Do. D 5.16 23.5 Do. E 4.58 19.54 D0.

5 parts of di(2-ethylhexyl) sebacate as the starting ma- It is clear from the data in Table I that only the prodterial. The product was an excellent synthetic lubricating nets of the present invention are free of supercooling oil. properties. Moreover, the products of this invention EXAMPLE 111 Example I was repeated except that a mixture of 90 parts of di(3,5,5-trimethylhexyl) sebacate and 10 parts of di(2-ethylhexyl) sebacate was employed, and the heating at 150 C. was continued for 6 hours. The product was an excellent lubricating oil.

EXAMPLE IV Example I was repeated except that in place of the 15 parts of di(2-ethylhexyl) sebacate, 15 parts of the diester of sebacic acid and Alphanol 79 was employed. Alphanol 79 is a commercial mixture of primary aliphatic alcohols containing from 7 to 9 carbon atoms per molecule, a substantial proportion of which are alphamethyl substituted primary aliphatic alcohols. The prodnot was an excellent synthetic lubricating oil.

EXAMPLE V A mixture of diesters comprising 85 parts of di(3,5,5- trimethylhexyl) adipate and 15 parts of di(2-ethylhexy1) sebacate was subjected to the process described in Example I. .The product was an excellent synthetic lubricating oil.

EXAMPLE VI A mixture of diesters comprising parts of di(3 ,5,5- 75 have, in general, better viscosity and flash point characteristics than products A, B, C, D, and E.

In the foregoing examples, the following alternative method of working up the reaction products may be employed. The reaction mixture is allowed to cool to 85 C. and hydrochloric acid (10 parts by volume of concentrated acid in parts by volume of water) is added with stirring. When cold, the mixture is diluted with 100 parts by volume of a gasoline fraction boiling between 70 C. and C., and the resulting organic layer is separated, washed with parts by volume of 2 'N hydrochloric acid and then with 10 parts by volume of water. The acid content of a small portion of the organic layer is determined and the bulk of the organic layer treated with 1.1 equivalents (based on its acid content) of an aqueous isopropyl alcohol solution of caustic soda. The aqueous solution is separated from the organic layer which is then washed with water until the washings are neutral, dried azeotropically, stripped of the gasoline by distillation under reduced pressure and finally stripped of other volatile by-products by distillation at 0.5 mm. of mercury at a bath temperature of 230 C.

EXAMPLE VIII One part of sodium was added to a mixture of 85 parts of di(3,5,5-trimethylhexyl)' sebacate and parts of di(2-ethylhexyl) sebacate at room temperature, the reaction vessel flushed out with nitrogen and the mixture heated with stirring to 150 C., at which temperature it was maintained for 1 /2 hours. allowed to cool to to C. and hydrochloric acid (10 parts by volume of concentrated acid in parts by volume of water) was added with stirring. When cold the mixture was diluted with 100 parts by volume of a gasoline fraction boiling between 70 C. and C., the organic layer separated, washed with parts by volume of 2N hydrochloric acid and then with 10 parts by volume of water and dried by azeotropic distillation. 1 Four parts of concentrated sulfuric acid (98%) and ethylene glycol in a quantity equivalent to 2.2 times the 1 amount of organic acids present in the mixture, were then added. This mixture was refluxed in a Dean and Stark apparatus until water evolution ceased. The reaction mixture was-cooled and washed with 250 parts by volume of saturated sodium bicarbonate solution to re move mineral acid. Any organic acidic material was then removed by washing with aqueous alcoholic caustic soda and then with water. The organic solution was dried azeotropically, the gasoline removed and the residue stripped free of alcohols by distillation at 4 mm. Hg pressure to a bath temperature of 200 C. The product was an excellent synthetic lubricating oil.

EXAMPLE IX Example VIII was repeated except that- 2' parts of I sodium and a quantity of ethylene glycol equivalent to twice the amount of organic acidspresent inthe mixture were employed. The product was an excellent synthetic lubricating oil.

EXAMPLE X One part of sodium was added to a mixtureof85 parts of di(3,5,5-trimethylhexyl) sebacate and 15 parts of di(2-ethylhexyl) sebacate and'the mixture heated, acidi-" fied, diluted, washed and dried as in Example VIIL" EXAMPLE XI Example X was repeated using 2 parts of sodium. The

product was an excellent synthetic lubricating oil. The W properties of the products of Examples VIII through XI are given in Table II. V

The mixture was then 5 the present compositions.

lubricating oils and compositions thereof. Where very high load-carrying capacity is required, an extreme pressure additive maybe added. A suitable type of extreme pressure additive for the present synthetic lubricating oils are the trialkyl, triaryl, or trialkaryl phosphates, such as tricresyl phosphate. Extreme'p'ressure agents of the haloalkanephosphonate type, such as monobutyl trichloromethanephosphonate and its amine salts, e. g., its salt with di(2ethylhexyl) amine, are also suitable in some cases. Among other materials which can be blended into the synthetic lubricating oils of the present invention to obtain special properties may be mentioned the complex ether-esters produced by condensing alkylene oxides, such-as ethylene or propylene oxide, with carboxylic acids, such as sebacic acid, and the 'ethers and esters of such complex ether-esters.

Antioxidants, particularly of the phenolic type, may be added to the present synthetic lubricating oils and compositions thereof. Preferably such antioxidants are not volatile at the highest temperature prevailing under the conditions of use. are suitable antioxidants.

The products of the present invention are particularly suitable as base oils for lubricating compositions intended for use in aircraft instruments and aircraft gas turbine bearings. A suitable lubricating composition for such use comprises a major proportion of a synthetic lubricating oil of the present invention, a polymeric ester of an acrylic acid, and a salt of an aromatic acidic compound with a metal'of group II of the periodic table.

The polymeric ester of an acrylic acid functions mainly as a .pour point depressor and viscosity index improver. Preferably, the polymer employed has an average molecular weight of not greater than 25,000, those polymers having an average molecular weight between about 400 and about 1000 being most suitable. Polymers having an average molecular weight between about 1000 and about 15,000 are also very useful. The preferred esters, the polymers of which are employed in the present compositions, are the esters of acrylic acid or an alpha-alkyl acrylic acid (preferably in which the alkyl group contains from about 1 to about 5 carbon atoms) and an alcohol of from about 1 to about 20 carbon atoms. Typical suitable esters include the methyl, ethyl, n-propyl, 'isopropyl, isobutyl, lauryl, phenyl and benzyl esters of acrylic, methacrylic, alpha-ethylacrylic acid, alpha-propylacrylicacid, and the like. Polymers of acrylic acid esters and methacrylic acid esters suitable for use in the present lubricating compositions are readily available as commercial products and are sold under the trade name Acryloid. They are generally available as concentrated dispersions in a solvent, and these concentrated dispersions can be used as such in the compounding of The polymers employed may be homo-polymers of a single ester or copolymers of a Although the synthetic lubricating oilsof the present invention are superior lubricants to the mixtures of diesters from which they are derived, nevertheless, for certain applications they require the addition of additives such as thickeners, anti-oxidants, anti-corrosive agents and anti-lacquering agents.

In some cases it may be-desirable to add small quantities of mineral lubricating oils-to the present synthetic mixture of such esters, and the term polymer as used herein is intended to be construed accordingly. The polymers are used in the present compositions in an amount of from about 2 to about 30%, and preferably from about S'to about 15%, by Weight based on the composition.

The metal salt employed in the present compositions 1; functions to increase the oxidation stability and thermal The alkylated phenols and diphenols of bearings.

stability of the lubricating composition under high temperature conditions of working and prevents lacquering Of the group I metals, zinc and calcium are the most suitable for the present purposes, but beryllium, magnesium, strontium, cadmium, barium or mercury salts can also be used. The aromatic acidic com- 1 pound employed can be either an aromatic carboxylic The term aromatic carboxylic acid acid or a phenol. is used herein to denote an aromatic carboxylic acid in which the carboxyl radical is attached directly to the aromatic nucleus. The aromatic acidic compound employed should have oleophilic properties to insure that the metal salt employed is suffi ciently soluble in the ester-polymer mixture to allow a metal content in the finished composition of between about 0.01% and about 1.0% by weight. Clearly, if a high metal content is desired a more oleophilic aromatic acidic compound should be used. Normal or basic salts or mixtures of normal and basic salts can be employed.

Representative aromatic carboxylic acids, the group II metal salts of which are suitable for use in the present compositions, include: benzoic acid, naphthoic acid, ptertiary-butylbenzoic acid, 2,4-ditertiary-butylbenzoic acid, diisopropylsalicyclic acids, octylsalicyclic acids, pentadecenylsalicyclic acids, octadecylsalicylic acids, stearyl salicylic acids, and octyl 4-hydroxybenzoic acids. The salts of alkyl hydroxybenzoic acids in which the alkyl group contains at least 8 carbon atoms are particularly suitable. Salts of mixtures of alkyl hydroxybenzoic acids, such as a mixture obtained by reacting salicylic acid or 4-hydroxybenzoic acid with a mixture of alkenes, e. g., a mixture of alkenes obtained by the cracking of parafiin wax, or with a mixture of alcohols in the presence of a suitable condensing agent, such as 90-98% sulfuric acid or zinc chloride. Similarly, salts of a mixture obtained by alkylating a phenol with such a mixture of alkenes or alcohols and converting the resulting alkyl phenols into alkyl salicylic acids by the Kolbe-Schmidt reaction can also be used.

Representative phenols, the group II metal salts of which are suitable for use in the present compositions, include: phenol, the naphthols, the cresols and the higher alkylated phenols, such as the amyl, octyl, nonyl, decyl, tetradecyl, pentadecenyl and octadecyl phenols, and the like. Salts of mixtures of alkyl phenols, for example, those made by the alkylation of a phenol with mixtures of alkenes, are preferred because of their lower melting points as compared with those of pure alkyl phenols. Mixtures of alkenes derived from paralfin wax by cracking or from higher fatty alcohols by dehydration are suitable starting materials for the manufacture of such mixtures of alkyl phenols. More than one alkyl or alkenyl group can be present in the phenol as in the case of compounds made by the dior tri-alkylation of phenols with alkenes, alkyl halides, alcohols or ethers, or of compounds made by the mono-alkylation of, for example, a cresol, a xylenol, carvacrol or cardanol. Other nuclear substituents may be present provided that they do not unduly reduce the oil-solubility of the phenol. Thus, halogen, alkoxy, alkyl mercapto and alkyl amino groups can be present.

Among the salts of phenols with group II metals, those derived from condensation products of certain hydrocarbon substituted phenols with an aldehyde, such as formaldehyde or acetaldehyde, are particularly etfective. More particularly, these condensation products are those produced from a hydrocarbon substituted phenol containing at least four carbon atoms in the substituent and capable of reacting with formaldehyde or acetaldehyde to give resinous condensation products, by reacting such phenol with formaldehyde or acetaldehyde or a polymer thereof, such as paraformaldehyde. These condensation prod- 'ucts can be converted into salts by reaction with basic compounds of group H metals, or the salts can be prepared directly by carrying out the condensation reaction in the presence of a basic compound of a group H metal,

preferably in the presence of an inert diluent.

A particularly useful salt for use in the present compositions can be made as follows, the parts referred to being parts by weight.

Sixty parts of para-octyl phenol are stirred into 260 parts of a solvent refined mineral lubricating oil containing 1 part of water, and 9.7 parts of calcium hydroxide and 10.1 parts of paraformaldehyde are added. The mixture is heated to C., the temperature then raised to C. over a period of 30 minutes and held at 95 C. for a further hour. The mixture is then filtered hot to yield aconcentrate having a sulfated ash content of 4% wt. This concentrate is referred to in the following examples as Concentrate A.

Other elfective metal salts are the Zinc salts of alkylated salicylic acids containing from about 12 to about 20 carbon atoms in the alkyl group. A particularly efiective compound is the zinc salt of a mixture of alkyl salicylic acids made by alkylating phenol with a mixture of alkenes containing 14 to 18 carbon atoms in the molecule and converting the resulting alkyl phenols into the corresponding salicylic acids by the Kolbe-Schmidt reaction.

Typical lubricating oil compositions based on the synthetic lubricating oils of the present invention are set forth in the following examples:

EXAMPLE XII Ten parts of a mixture of equal parts of di(3,5,5-trimethylhexyl) sebacate and Acryloid 710 were subjected to a shearing action by passage through an injector nozzle and then mixed with 86.85 parts of the product of Example I. 3.15 parts of the mineral oil solution of a calcium salt of a para-octyl phenol-paraformaldehyde condensation product referred to above as Concentrate A were then blended in to yield a lubricating composition suitable for use in gas turbine bearings. It had a viscosity at 210 F. of 8.2 centistokes. The Acryloid 710 used in this example is a high molecular weight polymerization product of the esters of methacrylic acid and cetyl and lauryl alcohols. It has the following representative physical properties:

Specific gravity (60 F./60 F.) 0.906 'Flash point, C. O. C., F. (when diluted with three parts of a 400 F. flash point mineral oil to decrease the viscosity and prevent local overheat- 96.85 parts of the product of Example I with 3.15 parts of Concentrate A referred to above. It had a viscosity at 210 F. of 5.4 centistokes.

We claim as our invention: 1. A synthetic lubricating oil prepared by a process comprising heating a mixture of a substantial amount of each of di(3,5,5-trimethylhexyl) sebacate and di(2- ethylhexyl sebacate, said mixture containing not less than 5 parts of each diester per parts by weight of said mixture, with from about 0.5% to about 2.5% by weight,

based on the mixture of sebacate esters, of sodium to a temperature of from about 100 C. to about 200 C.

2. A synthetic lubricating oil composition comprising a major proportion of the synthetic lubricating oil of claim 1, a polymer of an ester of an alpha, beta-olifinically-unsaturated acid,and an amount of alca'l'cium salt of a "1:12.:

95:5, with from about 0.5% to about 2.5% 'by weight,

1 based on the mixtures of sebacate esters, of sodium to a temperature of from about 100 C. to about 200 C. for a period of from about 1 to about hours. 4.-A synthetic lubricating oil prepared by: a process 4. comprising heating a mixture of a substantial amount of .each of di(3,5,5-trimethylhexyl) adipate and 'di(2-ethylabove the melting point of said alkali metal and below the temperature at which the mixture of diesters decomposes, acidifying the resulting reaction mixture thereby liberating organic acids from alkali metal salts thereof formed as by-products of the heating operation, and adding to the reaction mixture a polyhydric saturated aliphatic alcohol, whereby esters of said polyhydric saturated aliphatic alcohol and said liberated organic acids areformed L in the reaction mixture.

hexyl) sebacate, said mixture containingnot less than based on the mixture of esters, of sodium to a temperature offrom about 100 C.-to about 200 C.

5 parts of eachdiester per/100 parts by-weight -of said mixture, with from about 0.5% to about 2.5% by weight,

9. A synthetic lubricating oil prepared by a process comprising heating a mixture of asubstantial amount of each of at least two normally liquid diesters of at least one aliphatic dicarboxylic acid in which the carboxyl radicals are separated by at least 1 carbon atom and mor1ohydric alcohols of at least 3 carbon atoms, said mixture containing not less than 5 parts of eachdiester per 100 parts by weight of said mixture, with an alkali 'metal to a temperature above the melting point of said alkali metal and below the temperature at which the mixture of diesters decomposes.

5. A synthetic lubricating oilprepared by'a process each of di(3,5,5trimethylhexyl) sebacate and di(2-ethylhexyl) sebacate, said mixture containing not less than 5 parts of each diester per 100 parts by weight of said comprising heating a mixture of a substantial amount of 10. A synthetic lubricating oil prepared by'a process comprising heating a mixture of a substantial amount of each of at least two normally liquid diesters of at least one dicarboxylic acid in which the carboxyl radicals are separated by at least 1 carbon atom and monohydric i alcohols of at least 3 carbon atoms, said mixture conmixture, with sodium to a temperature of from about 100 C. to about 200 C., acidifying the resulting reaction mixture, thereby liberating organic acids from sodium salts thereof formed as by-products of the heating operation, and adding to the reaction mixture ethylene glycol, whereby'esters of ethylene glycol and said liberated'organic acids are formed in the reaction mixture.

6. A synthetic lubricating oil prepared by a process comprising heating a mixture of a substantialamount I of each of at least two normally liquid diesters of at least one-saturated aliphatic dicarboxylic acid inwhich the carboxyl radicals are separated by a chain of from about 4 to about 8 carbon atoms and branched-chain per 100 parts by Weight of said mixture, with sodium to alkanols of from about 4 to about carbon atoms, said mixture containing not less than 5 parts of each diester tain ing not less than 5 parts of each diester per 100 parts by'weight of saidmixture, with an alkali metal to a tem'-' perature'above the melting point of said alkali metal and below the temperature at which the mixture of diesters decomposes, acidifying the resulting reaction mixture,

thereby liberating organic acids from alkali'metal salts thereof formed as by-products of the heating operation, and adding to the reaction mixture a polyhydric alcohol. whereby esters of said polyhydric alcohol and said 12? erated organic acids are formed in the reaction mixture.

11. A synthetic lubricating oil prepared by a process comprising heating a mixture of a substantial amount of each of at least two normally liquid diesters of at least one saturated aliphatic dicarboxylic acid in which the carboxyl radicals areseparated by a chain of from about 4'to about 12 carbon atoms and alkanols of from about 4 a temperature above the melting point of sodium and below the temperature at which themixture of diesters de- 7; 'A synthetic lubricating oil prepared by a process each of at least two normally liquid diesters of at least comprising heating a mixture of a substantial amount of 4 to about 8'carbon atoms and branched-chain alkanols a of from about 4'to about 20 carbon atoms, said mixture containing not less than 5 parts of each diester per 100 parts by Weight of said'mixture, with sodium to a temperature above the melting point of sodium and below the temperature at which the mixture of diesters decomposes, acidifying the resulting reaction mixture, thereby liberating organic acids from sodium salts thereof formed as by-products of the heating operation, and adding to the reaction mixture a dihydric saturated aliphatic alcohol of from about 2 to about carbon atoms, whereby esters of said dihydric saturated aliphatic alcohol and said liberated organic acids are formed in the reaction mixture.

8. A synthetic lubricating oil prepared by aiprocess comprising heating a mixture of a substantial amount of less thanS parts of each diester per 100 parts byweight of said mixture, with an alkalimetalto a temperature to about 20 carbon atoms, said mixture containing not less than 5 parts of each diester per 100 parts'by weight of said mixture, with an alkali metal to a temperature above the melting point of said alkali metal and below. the temperature at which the mixture of diesters decomposes.

12. A synthetic lubricating oil composition comprisinga major proportion of the synthetic lubricating oil of claim 11, a polymer of an ester of an alpha, betaolefinically unsaturated acid, and an amount of a group II metal salt of a condensation product of an alkyl substituted phenol, said alkyl group having at least 4 carbon atoms, and an aldehyde sutficient to give a metal content to'the composition of fromabout 0.01% to about 1.0%

by weight.

13. A synthetic lubricating oil composition comprismg a major proportion of the synthetic lubricating oil of claim 11, a polymer of an ester of an alpha, beta-olefinicallyunsaturated acid, and an amount of a group 11 metal salt of an alkylated salicylic acid in which the alkyl group contains from about 12 to about 20 carbon each of at least two normally liquid diesters of at least one saturated aliphatic dicarboxylic acid in. which the atomssufiicient to give a metal content to the composition of from about 0.01% to about 1.0% by Weight.

14. A synthetic lubricating oil prepared by a process comprising heating a mixture of a substantial amount of each of at least two normally liquid diesters of at least one dicarboxylic acid in which the carboxyl radicals are separated by at least 1 carbon atom and monohydric alcohols of at least 3 carbon atoms, said mixture containing not less than 5 parts of each diester per parts by weight of said mixture, with an alkali metal to a tem- 7 5 perature above the melting point of said alkali metal and 13 below the temperature at which the mixture of diesters decomposes.

15. A synthetic lubricating oil composition comprising a major proportion of the synthetic lubricating oil of claim 14, a polymer of an ester of an alpha, beta-olefinically unsaturated acid, and a group II metal salt of an aromatic acidic compound selected from the group consisting of aromatic carboxylic acids and phenols.

References Cited in the file of this patent I Organic Reactions, volume 1, pages 274-275, 294- 295, Wiley, New York, 1942. 

11. A SYNTHETIC LUBRIATING OIL PREPARED BY A PROCESS COMPRISING HEATING A MIXTURE OF A SUBSTANTIAL AMOUNT OF EACH OF AT LEAST TWO NORMALLY LIQUID DIESTERS OF AT LEAST ONE SATURATED ALIPHATIC DICARBOXYLIC ACID IN WHICH THE CARBOXYL RADICALS ARE SEPARATED BY A CHAIN OF FROM ABOUT 4 TO 12 CARBON ATOMS AND ALKANOLS OF FROM ABOUT 4 TO ABOUT 20 CARBON ATOMS, SAID MIXTURE CONTAINING NOT LESS THAN 5 PARTS OF EACH DIESTER PER 100 PARTS BY WEIGHT OF SAID MIXTURE, WITH AN ALKALI METAL TO A TEMPERATURE ABOVE THE MELTING POINT OF SAID ALKALI METAL AND BELOW THE TEMPERATURE AT WHICH THE MIXTURE OF DIESTERS DECOMPOSES.
 12. A SYNTHETIC LUBRICATING OIL COMPOSITION COMPRISING A MAJOR PROPORTION OF THE SYNTHETIC LUBRICATING OIL OF CLAIM 11, A POLYMER OF AN ESTER OF AN ALPHA, BETAOLEFINICALLY UNSATURATED ACID, AND AN AMOUNT OF A GROUP II METAL SALT OF A CONDENSATION PRODUCT OF AN ALKYL SUBSTITUTED PHENOL, SAID ALKYL GROUP HAVING AT LEAST 4 CARBON ATOMS, AND AN ALDEHYDE SUFFICIENT TO GIVE A METAL CONTENT TO THE COMPOSITION OF FROM ABOUT 0.01% TO ABOUT 1.0% BY WEIGHT. 